Conventional techniques for locating IEEE 802.11 emitters (e.g., access points as well as laptops with IEEE 802.11 capability and other such clients) are based on measuring the amplitude of the 802.11 emitter with a portable receiver, and moving around to find the direction in which the amplitude increases. The general assumption is that the stronger the signal amplitude, the closer the 802.11 emitter is believed to be. Several commercial devices were developed for this purpose (e.g., Yellowjacket® 802.11b Wi-Fi Analysis System).
There are a number of problems associated with such amplitude-based techniques for locating 802.11 emitters. For instance, the techniques tend to be highly inaccurate due to the incidence of RF multipath created by the RF waveforms emanating from the 802.11 emitters. These waveforms bounce off conductive objects or surfaces in the environment, which causes multiple false readings on increased amplitude (false directions) that then disappear as the user leaves the multipath. Thus, conventional amplitude-based locationing techniques will create many false high amplitude paths to the target that will be incorrect, and will not work in a high multipath environment, such as a neighborhood (e.g., street scene) or building (e.g., home, office building, or café).
There is a need, therefore, for techniques that allow for the detection, identification, direction finding, and geolocation of wireless emitters in a given environment.